1. Field of the Invention
The root system of a tooth can include from one to four major canals extending generally upward from an apical opening at the bottom of the tooth and a plurality of accessory or auxiliary canals opening laterally from the major canals. Conventional root canal therapy comprises cleaning and shaping of the major canals followed by filling the root system in a manner to obturate both the major and accessory canals. In this way, the intrusion of body fluids into the canal system is prevented and possible inflammation is avoided. It is particularly important that the major and accessory canals be completely sealed in order to maintain the integrity of the tooth.
Three techniques for performing root canal therapy are in widespread use today. The first technique, referred to as lateral condensation, relies on inserting a plurality of gutta percha cones to fill the major canal. A first (master) cone is placed to seal the apical opening and a number of accessory cones are used to fill the remainder of the canal. A sharp steel instrument is used to compress the cones and spread the gutta percha in a lateral direction to fill the major and accessory canals. The instrument creates large lateral forces which can fracture the tooth in the absence of extreme care. Moreover, the lowermost cone can be forced through the apical opening and into the surrounding tissue, causing inflammation. In addition, the gutta percha frequently adheres to the compression instrument and, unless the instrument is withdrawn cautiously, the filling will be loosened or displaced as the instrument is removed.
A second technique, referred to as the heated gutta percha technique, relies on the use of a high temperature probe to melt the gutta percha in situ. A cold, lubricated instrument is then used to compact the filling material and to flow such material into the accessory canals. One or more gutta percha cones are emplaced in the major canal and treated in such a manner until the root canal system is filled. Although generally an improvement over the lateral condensation technique, the heated gutta percha technique also suffers from drawbacks. If the heated probe is not removed at precisely the right moment, the melted gutta percha will adhere to the probe and be removed from the tooth. Use of the compacting instrument can apply excessive lateral force and cause tooth fracture or cause the material to pass through the apical opening. Finally, if the heated probe is removed too soon, the gutta percha may not uniformly melt and some of the accessory canals may not be filled.
The third approach to root canal therapy involves the use of compounded pastes and fillers which are packed or injected into the root canal system. Numerous specific techniques have been developed, and the techniques generally suffer from inadequate materials, i.e., the filling materials may be difficult or impossible to remove from the canal, and a tendency to overfill the canal system causing material to flow through the apical opening and into the surrounding tissues. Either of these problems can necessitate oral surgery to correct.
It would thus be desirable to provide a method and system for filling the root canal system which assures that sufficient material is implanted to fully obturate the major canal and all accessory canals, avoids over filling the canal and causing the incursion of material into the surrounding tissues, and avoids the necessity of compacting the filling material by inserting a compaction tool into the major canal and possibly fracturing the tooth by causing excessive lateral forces.
2. Description of the Prior Art
U.S. Pat. Nos. 3,899,830 and 3,949,479 to Malmin describes a system for filling root canals with gutta percha filling points. The filling points may be melted after placement in the tooth by use of an ultrasonic heating device. British Pat. No. 214,497 describes a gutta percha filling point. U.S. Pat. No. 4,357,136 to Herskovitz et al. describes a syringe for injecting heated thermoplastic materials into a prepared root canal.